1. Field of the Invention
The present invention relates to an information recording medium, an information recording/reproduction system apparatus and an information recording/reproduction method for managing AV (audio/video) data by using a file structure.
2. Description of the Related Art
An optical disk is a type of information recording medium which has a sector structure. In recent years, the recording density and the capacity of an optical disk have been increased, and optical disks usable in multimedia applications have been developed. Accordingly, it has become important to increase the access speed so that it is possible to interactively reproduce data using a plurality of data sets. A DVD-video disk has been developed as an optical disk capable of interactively reproducing video titles. A DVD-video disk contains AV data which includes a plurality of MPEG program streams and control data which is used for controlling the reproduction of the AV data.
Referring to a directory structure illustrated in FIG. 9 and a data structure illustrated in FIG. 10, the structure of directories recorded on a DVD-video disk and the relationship between the AV data and the control data will now be described by way of an example. A DVD-video file 908 is recorded using a predetermined file name under a predetermined directory so that a DVD player can easily access data. In particular, a video directory 902 is created under a root directory 901.
The DVD-video file 908 includes AV data 907 and control data 906. The AV data 907 and the control data 906 are recorded under the video directory 902. In particular, the AV data 907 is recorded as a file 904 named “Video.AVD”, and the control data 906 therefor is recorded as a file 903 named “Video.IFO”. A file 905 named “File-A.DAT”, which is used in personal computers, and the like, is recorded in a location other than under the video directory 902. Therefore, the DVD player will not erroneously reproduce PC data.
Typically, the AV data 907 includes a plurality of video objects (hereinafter, referred to as “VOBs”). In the example illustrated in FIG. 10, the AV data 907 includes VOB 1009 and VOB 1010. The VOB 1009 and the VOB 1010 are both VOBs but differ from each other in terms of the conditions under which video data and audio data represented by the VOBs are compressed or encoded. For example, the VOB 1009 may be AV data of a news program which has been compressed by the MPEG1 data compression scheme, while the VOB 1010 may be AV data of a live baseball program which has been compressed by the MPEG2 data compression scheme. The control data 906 includes a program 1011 for controlling the reproduction of the AV data 907 and VOB management information 1012 which is used for managing the information of each VOB. The program 1011 includes a program 1001 for controlling the reproduction of the VOB 1009 and a program 1002 for controlling the reproduction of the VOB 1010. The programs 1001 and 1002 each specify a reproduction start address 1005 and a reproduction end address 1006 of the VOB. The reproduction start address 1005 and the reproduction end address 1006 are specified, respectively, by identification information of each of the VOBs 1009 and 1010 of the AV data 907 and the number of relative bytes with respect to the leading address of each of the VOBs 1009 and 1010. In the example illustrated in FIG. 10, the programs 1001 and 1002 are registered. The program 1001 is programmed to reproduce a portion 1007 of the VOB 1009, and the program 1002 is programmed to reproduce a portion 1008 of the VOB 1010. Thus, program data (a VOB) can be partially reproduced by specifying the reproduction start address and the reproduction end address of the VOB. VOB management information 1012 includes VOB management information 1003 for managing the information of the VOB 1009 and VOB management information 1004 for managing the information of the VOB 1010. Each of the VOB management information 1003 and 1004 includes various information for the VOB such as the type of TV broadcasting system, the resolution, the number of channels for audio data, the compression schemes for video data and audio data, information used for performing a search by specifying the time of AV data, information used for managing location information by GOPs (groups of pictures) defined in MPEG, and the data size of the VOB. A DVD-video disk having recorded thereon information which has the directory structure illustrated in FIG. 9 and the data structure illustrated in FIG. 10 is reproduced as follows. Application software can read out the control data 906 and interactively reproduce a plurality of VOBs by using a predefined program.
Referring to FIGS. 7A and 7B, the relationship between the physical structure of a DVD-RAM disk 700, which is a rewritable optical disk, and the logical volume space thereof will now be described. FIG. 7A illustrates the physical structure of the DVD-RAM disk 700. The DVD-RAM disk 700 includes a lead-in area 701, a DMA (defect management area) 702 for managing defects on the disk 700, a data area 718, and a lead-out area 716 which are arranged in this order from the inner periphery to the outer periphery of the DVD-RAM disk 700. Digital data is recorded in each of these areas, and the digital data is managed by a unit called a “sector”. The data area 718 includes a spare area 703 used for replacing defective sectors and an area 719 including a plurality of zones numbered from zone 0 to zone 47. In each zone, data is recorded in blocks of 2048-byte physical sectors.
Referring to FIG. 7B, the physical sectors are numbered with physical sector numbers (PSNs) starting from the inner periphery of the disk 700. Physical spaces 717 of the disk 700 are specified by PSNs. On the other hand, the space in which user data can be recorded is defined as a volume space 720 which includes a plurality of sectors which are numbered with logical sector numbers (LSNs). In other words, the volume space 720 is equal to the physical space 717 minus the lead-in area 701, the DMA 702, the spare area 703, a defective sector 711, a guard area 715 provided between two adjacent zones, and the lead-out area 716. The defective sectors 711 are sectors which have been detected as being defective by a certification operation performed during an initialization of the disk 700. The PSNs of the defective sectors 711 are registered and managed in a PDL (primary defect list) (not shown) provided in the DMA 702. A defective sector 721 which have been detected as being defective while recording data onto the disk 700 are replaced with spare sectors from the spare area 703 by a linear replacement method and registered in an SDL (secondary defect list) (not shown) provided in the DMA 702.
Next, FIG. 8 illustrates an example of a data structure which would result when the various files as mentioned above are recorded on the rewritable disk 700 by using a volume file structure 800 as defined in the ECMA 167 standard. The upper portion and the lower portion of FIG. 8 correspond to the inner periphery and the outer periphery of the disk 700, respectively. Sectors in the volume space 720 are numbered with the logical sector numbers (LSNs) starting from the leading sector of the volume space 720. A volume structure area 801 includes recorded therein information which is used for logically handling the disk 700 as a volume, as well as location information of a space bit map 821, and location information of a file entry 822 of the root directory. While the file set descriptor is defined as a file structure according to the ECMA 167 standard, the file set descriptor is treated herein as a volume structure for the sake of simplicity. It is also assumed herein that files are accessed by using their logical sector numbers for the sake of simplicity, though they are typically accessed by using their logical block numbers.
A file structure area 802 is an area in which a descriptor for defining the file structure is recorded. The file structure area may be recorded in a distributed manner in the volume space 720. The space bit map 821 is a bit map which is used for managing, by blocks of sectors, free areas in the volume space 720 to which a file structure or data can be allocated. The space bit map 821 includes location information of unallocated areas 805 and 807. The file entry 822 includes a descriptor tag 851 indicating that the descriptor is a file entry, attribute information 852 which specifies attribute information of the file used by the file system, e.g., the recording date, and an allocation descriptor 853 for managing the recording location information of a file or a directory. The allocation descriptor 853 has the same data structure as that shown for an allocation descriptor 834. A series of continuous areas in which data is recorded is called an “extent”. An extent is specified by a length 865 thereof and a start location 866 thereof. A directory includes one or more file identifier descriptors, and a file identifier descriptor is recorded for every sub-directory or file which is registered in the directory. A file identifier descriptor 823 includes a descriptor tag 854 indicating that the descriptor is a file identifier descriptor, a file name 855 which specifies a file or a directory, and location information 856 of the file entry. Since the root directory 901 (FIG. 9) includes the video directory 902 and the File-A.DAT file 905, the file identifier descriptors 823 and 824 are recorded for the video directory 902 and the File-A.DAT file 905, respectively. Similarly, other directories and files are managed by file identifier descriptors and file entries 825 to 830.
Next, a method for managing the AV data 907 will be described. Typically, AV data has a large data size and is divided into a plurality of portions which are recorded in a plurality of areas on the disk in a distributed manner. For example, when AV data having an average data rate of 5 Mbps (megabits/sec) is recorded for one hour, the size of the recorded data will be 2 GB (gigabytes). Moreover, after repeatedly editing, deleting and adding data, the free areas are typically scattered on the disk. On such a disk whose free areas have been scattered, new AV data is recorded in a distributed manner in a plurality of extents. In FIG. 8, the AV data is recorded in a distributed manner in extents 837, 839, 841 and 842. In such a case, since the volume file structure 800 does not manage the contents of the data to be recorded, a portion of a VOB 881 and a portion of a VOB 882 near the boundary therebetween will be recorded in the same extent (extent 841). The location information of these extents 837, 839, 841 and 842 is recorded in an allocation information area 803 by using allocation descriptors. Since an AV file, as compared to other files, requires a larger number of allocation descriptors to be registered, it may not be possible to register all the allocation descriptors in the file entry 830 which is limited to a size of 1 sector or less. Therefore, location information of the new allocation information area 803 is registered in the location information 862 of the allocation information area in the file entry 830. The allocation information area 803 has an allocation extent descriptor 831 in the leading position therein, followed by allocation descriptors 832, 833, 834 and 835 which are continuously registered immediately after the allocation extent descriptor 831. The allocation extent descriptor 831 has a descriptor tag 863 indicating that the descriptor is an allocation extent descriptor and a length 864 of the allocation descriptor which is registered immediately after the allocation extent descriptor 831. The allocation descriptors 832, 833, 834 and 835 specify the respective extents 837, 839, 841 and 842 of the AV data 907 by the length 865 and the start location 866 thereof.
Next, a method for reproducing the AV data 907 based on the programs 1001 and 1002 of the control data 906 will be described. The programs 1001 and 1002 specify the reproduction start address 1005 and the reproduction end address 1006 of the VOB by the relative address of the AV data 907 with respect to the leading address of the AV data 907. Therefore, in order to find the recording location of the AV data to be actually reproduced, the allocation descriptor in the allocation information area 803 is read out and the logical sector number is calculated therefrom. The reproduction start location is obtained by adding together the lengths 865 of the extents which are registered in the allocation descriptors sequentially starting from the allocation descriptor 832. In particular, when the accumulated length equals the reproduction start location in the AV data, the logical sector number at that time represents the reproduction start location on the disk. The AV data is reproduced by using the allocation descriptor which corresponds to the logical sector number thus obtained. The reproduction end location is calculated in a manner similar to that for the reproduction start location. The reproduction of the AV data ends when the accumulated length of the extents 837, 839, 841 and 842 equals the reproduction end address.
However, with the above-described volume file structure 800, the reproduction of AV data may be discontinuous when the AV data is edited because the data rate information of the recorded areas is not managed. If a table for managing the data rate is created for every recorded area, the size of the table information will be large such that it cannot be managed by a consumer product whose memory size is limited.